@Porky - the single best do it now idea in the discussion is to get that massive file off you desktop just for computer health/function.
It’s quick; make an alias of your encompassing folder of pics using the popup menu from a right-click on the folder (there are other ways, doesn’t matter how). Then drag the original to wherever you want (documents is a good choice. The alias stays on your desktop and lets you open the file. Your iMac May even run faster. One last idea. Rename your folder with the pics before making the alias, by inserting a space at the beginning of the name. Then the folder will be the first one listed in the place you store it and so easy to find.
Looks like your still contemplating and evaluating possibilities... that’s excellent!
Best of luck my friend.